/*
 * Copyright 1999-2009 The Apache Software Foundation.
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 */
package org.apache.xml.security.keys.keyresolver.implementations;

import java.security.Key;
import java.security.PublicKey;
import java.security.cert.X509Certificate;

import javax.crypto.SecretKey;

import org.apache.xml.security.encryption.EncryptedKey;
import org.apache.xml.security.encryption.XMLCipher;
import org.apache.xml.security.encryption.XMLEncryptionException;
import org.apache.xml.security.keys.keyresolver.KeyResolverSpi;
import org.apache.xml.security.keys.storage.StorageResolver;
import org.apache.xml.security.utils.EncryptionConstants;
import org.apache.xml.security.utils.XMLUtils;
import org.w3c.dom.Element;

/**
 * The <code>EncryptedKeyResolver</code> is not a generic resolver.  It can 
 * only be for specific instantiations, as the key being unwrapped will 
 * always be of a particular type and will always have been wrapped by 
 * another key which needs to be recursively resolved.
 *
 * The <code>EncryptedKeyResolver</code> can therefore only be instantiated
 * with an algorithm.  It can also be instantiated with a key (the KEK) or 
 * will search the static KeyResolvers to find the appropriate key.
 *
 * @author Berin Lautenbach
 */

public class EncryptedKeyResolver extends KeyResolverSpi {

    /** {@link org.apache.commons.logging} logging facility */
    static org.apache.commons.logging.Log log = 
        org.apache.commons.logging.LogFactory.getLog(
                        RSAKeyValueResolver.class.getName());

    Key _kek;
    String _algorithm;

    /**
     * Constructor for use when a KEK needs to be derived from a KeyInfo
     * list
     * @param algorithm
     */
    public EncryptedKeyResolver(String algorithm) {		
	_kek = null;
        _algorithm=algorithm;
    }

    /**
     * Constructor used for when a KEK has been set
     * @param algorithm
     * @param kek
     */
    public EncryptedKeyResolver(String algorithm, Key kek) {		
	_algorithm = algorithm;
	_kek = kek;
    }
	
    /** @inheritDoc */
    public PublicKey engineLookupAndResolvePublicKey(
           Element element, String BaseURI, StorageResolver storage) {
        return null;
    }

    /** @inheritDoc */
    public X509Certificate engineLookupResolveX509Certificate(
           Element element, String BaseURI, StorageResolver storage) {
        return null;
    }

    /** @inheritDoc */
    public javax.crypto.SecretKey engineLookupAndResolveSecretKey(
        Element element, String BaseURI, StorageResolver storage) {
        if (log.isDebugEnabled()) {
  	    log.debug("EncryptedKeyResolver - Can I resolve " + element.getTagName());
        }

        if (element == null) {
            return null;
        }

        SecretKey key = null;
        boolean isEncryptedKey = XMLUtils.elementIsInEncryptionSpace(element,
                                 EncryptionConstants._TAG_ENCRYPTEDKEY);
        if (isEncryptedKey) {
	    log.debug("Passed an Encrypted Key");
	    try {
	        XMLCipher cipher = XMLCipher.getInstance();
	        cipher.init(XMLCipher.UNWRAP_MODE, _kek);
	        EncryptedKey ek = cipher.loadEncryptedKey(element);
	        key = (SecretKey) cipher.decryptKey(ek, _algorithm);
	    } catch (XMLEncryptionException e) {}
        }
		  	      
        return key;
   }
}
